Partial oxidation of hydrocarbons



J. w. MULLEN u, ETAL 2,722,553

PARTIAL OXIDATION OF HYDROCARBONS Nov. 1, 1955 Filed Aug. 30, 1952 2 Sheets-Sheet 1 0 NT F l REACTANT 5 4 c OLA w 6 a 3, FUEL COMBUSTION REACTION OXIDANT ZONE ZONE 7,

2 ouswcmms/ l l ZONE REACTANT l COOLANT F35 l 8 u l FUEL COMBUSTION RE ACTIO N OXIDANT ZONE 20m: 7

I0 OUENCHING i ZONE FUlEL 3 '6 COMBUSTION C TS OXIDANT 7/ 2 ZONE REA TAN COOLANT Mn [3. 7m 9W b): Mai AIL P /m qPM/AUL W ATTORNEYS Nov. 1, 1955 w, MULLE u, Er 2,722,553

PARTIAL OXIDATION OF HYDROCARBONS Filed Aug. 30, 1952 2 Sheets-Sheet 2 1.92 R EACTAN T COM BUSTION QUENCHI N 6 FUEL OXIDANT REACTDON ZONE Wfi ZONE I IF) COOLANT T COOLANT F1 5. REA TAR;3 1

H Q 2' FUEL a g QUENCHING OXIDANT v A ZONE [COMBUSTION 2 ZONE REACTION 20m:

i 6. REAOIANT 2 FUEL COMBUSTION 22 REACT'ON OXIDANT ZONE ZONE Z I l:

Fi REACTANT REACTANT I l 23 l 32 MM L FUEL COMBUSTION QUENCH |N6 OXIDANT zom: REACTION ZONE ZONE awe/ms M ATTORNEYS .gas whichis to be heated to reaction .temperature.

United States "Patent-f) PARTIAL OXIDATION OF HYDROCARB'ONS James W. Mullen II and John B. Fenn, Richmond, Va., assignors to Chemical'Construction Corporation, New York, N. Y., a corporation of'Delaware Application August 30, 1952, Serial No. 307,196

9 Claims. (Cl. 260-606) This invention relates to the transformation .of hydrocarbons into useful .oxidation products andparticularly to the partial oxidation of hydrocarbons.

The disadvantages of present methods for effecting oxidationof hydrocarbons to intermediate oxidation products arise to .a large extent from inherent difiiculties in bringing about rapid and uniform heat transfer to the reactant hydrocarbons and rapidand uniform cooling of reaction product-s. When .a gas is heated by means of a .heat exchanger wherein heat is supplied to one side of a wall or partition from a source such ascombustion gases,

steam, orhot liquids, the .heatis carried by conductivity through the wall and .is taken up on the other sideby the The heat transfer rates which are possible in such equipment are relatively small. Consequently, high temperature gradients and large surfaces are necessary. More important .for present considerations, however, is the fact thatthe heating of the reactant gas cannot be made uniform so that portions thereof are subjected to very high temperatures while other ,portions remain relatively cool .and :unreactive. .In addition, since the rate at which the reactant .gas can be heated up, and .later cooled ofli, is slow, many side reactions occur and the reaction of inter- .est may proceed further than is desirable with resultant loss in yield.

While improvement inheat transfer can 'be obtained by the direct mixing ofhot gases such as superheatedisteam or hot combustion gases with the reactant gas, therates :of mixing of gases under the conditions of prior methods are so slow that the uniformity and rapidity with which the reactant is brought to the desired reaction temperatures are .far short of those necessary to obtain optimum yields and freedom from side reactions. A result of these-conditions inherent in prior processes is that one portion of the reactant is subjected to excessive heating while another portion is insufiicient-ly heated, so that even though theaverage temperatures and times of heating are within the desired ranges .only a small proportion of the reactant is actually treated in accordance with such measured average conditions.

It is a principal object of the present invention to provide an improved method for the oxidation-of hydrocarbons to intermediate oxidation products whereby rapid and uniform heatingof reactants and cooling of reaction products is obtained.

Anotherobject of the invention is to provide an improved method for the .partialoxidation of hydrocarbons 'such as the oxidation .of methanetoformaldehyde, ethylene .to ethylene oxide, propane .and butane toacrolein and methacrolein respectively, .and the products of carbon monoxide and hydrogenand hydrocarbons.

Other objects and advantages of the invention will v appear. hereinafter.

Wehave found that very advantageous improvements in the thermal transformation .and partial oxidation of hydrocarbons can be obtained by introducing the hydrocarbons into "high temperature combustion 'productsof- 2,722,553 "Patented Nov. 1 5

ice

from a wall pressure'tap), to stagnation pressure f (e. g.

from a total heador "Pitot'tube or 'from;a static tapiwh'ere the velocity is very 1ow,.say in anupstreamenlargement in the duct) be about 1 to,2. Thus, inalductedburner exhausting 'to atmospheric pressure (14.7 p. s. .i. .a.) ,if the air and fuel are supplied at 'about'30 p.. s. i. .a. (or 15 p. s. i. gauge), sonic velocity will .obtain in the duct at the point ofsmallest area. However, it is not necessary that they be supplied at this high pressure if an appropriate nozzle is used together with a diffuser downstream from the nozzle throat. Thus air and fuel supplied at as low as 20 p. s.. i. .a. or'lower can 'be brought to.sonic velocity at .thethroat of a converging nozzle and thenexpanded back to atmospheric pressureprior toexhausting into the atmosphere. In this casethe static .Pressure at the throat ,of the nozzle would still be halfo'f the supply pressure or 10 p. s. i. a. but'lessthan atmospheric pressure.

The pump supplying the air wouldbe requiredntojeliver on'lyat20 p. .s. i. a. even though final, exhaustion wastat 14.'7 p. s. i. a. Inother words, the ratio ,of 1 to .2 for static absolute'pressure .to stagnation absolute pressure .in order to ,meet the requirements for sonic .ve'locity relates only to the pressures in the sonic zone and does not-necessarily relate to the. overall initial and finalpressures.

In cases where low pressures may favor a ,desired oxidation reaction it is possible to practice the invention, at subatmospheric pressures, by use of vacuum pumps or exhausters in'the downstream .end of 'theburuer reaction duct. Again the requirement of a '1. to 2,,pressuretratio for sonic velocity relates to the static andstagnationppressures in the sonic zone and not necessarily .overall.

Thus by burning gasoline, for example, with excess air in a chamber maintained at pressures higher .thaua'bout 15 pounds per square inch gauge, velotzitiesabove (2500 feet per second may be obtained. By workingat. higher pressures and using appropriate expanding nozzles, the velocity of the exhaust stream from the burnercambe much higher "than. 3000 feet per. second. .Ifsuchahigh velocity stream of'hot gases is broughtinto,confluencewith a stream of a reactanthydrocarbm extremely Iflpidand uniform mixing .of.the two streamsisobtained.resl ltingin rapid and uniform heating of the reactant. vrMoreoi/er, withappropriate configuration of the apparatustheresuiting stream of, mixed combustiongases andsreacta willretain a: very high velocity, sothat by controllingthe length of the reaction duct very precise .control\.of..-the

length of the time of reaction between the ,excessoxygen the tendency of the burners to oscillate, fiash'l'back, detonate, andblow out. By shielding the combustion-zone from pressure fluctuations these difficulties are eliminated. Moreover, the mass flow .of .combustion products from a'"burner exhausting at sonic velocity can'be controlled very closely so that the temperature of the resulting mixture of combustion products and reactants can be maintained very near to the desired level by merely controlling the mass flow of the reactant stream; This is likewise very desirable since the temperature coefiiizients of many of the reaction rates of interest are quite arge.

A further advantage is that in operating at high pressure a relatively small burner can provide a very large mass flow of combustion products and resultant heat release. For example, a ducted burner only two inches in diameter, two feet long, operating at a pressure of about 45 pounds per square inch gauge, and using a hydrocarbon fuel such as gasoline, will burn as much as a pound and a quarter of air per second resulting in almost 1500 B. t. u.s per second of heat release.

Many other advantages accrue to the use of burners operating at pressures sutficiently high to maintain critical flow conditions at the exhaust. Such burners are conveniently referred to as being choked or operating under choking conditions. A burner can also be caused to choke by decreasing the pressure of the chamber into which it is exhausting rather than raising the pressure in the combustion zone.

mixed with the hot combustion gas at high velocity;

Fig. 4 shows an apparatus in which the reactant is introduced together with the oxidant and fuel and coolant is introduced into the gas stream after cooling by expanslon;

Fig. 5 shows an apparatus in which the reactant and the coolant are successively introduced prior to expansion of the gases to high velocity;

Fig. 6 illustrates an embodiment in which the reactant 1s lntroduced at the point of expansion of the gas to high velocity; and

Fig. 7 illustrates apparatus in which a second supply of reactant serves as the coolant.

In Fig. 1 gaseous fuel and oxidant are introduced under pressure into one end of duct 1 which contains baffie 2'on which a flame is stabilized. Combustion of the fuel and oxidant is completed in the remainder of duct 1 which terminates in nozzle 3. As long as the static pressure in duct 1 is approximately twice that in cham-" her 4, the velocity of the combustion products in the throat of nozzle 3 will be sonic. A reactant stream is injected through tube 5 to mix with the high velocity stream of hot combustion products, the relative mass flows of the exit end of the duct. The time for mixing and reaction is thus determined by the length of duct 1 downstream from the injection point of the reactant to the exit end 9 of the duct 1. So long as the pressure in the combustion zone is roughly twice that in the quenching chamber 10, the resulting mixture of combustion products, reactants, and desired reaction products will leave the duct 1 at sonic velocity. However, because the temperature of the mixture will be lower on account of the presence of colder reactants, the velocity, though still sonic, will be somewhat lower than in the case illustrated in Fig. l. The reason for this lower velocity is, of course, that the sonic velocity of a gas stream is determined by temperature to a large extent. The stream of combustion gases, reactants and reaction products encounters a coolant spray from nozzle 11 which quenches further reaction, after which the mixture is led to suitable separating means not shown.

Fig. 3 shows a variation of the invention in which a liquid fuel can be used by introducing it as a spray from the nozzle 12 into the incoming stream of oxidant in the combustion chamber 13. After combustion under pressure in chamber 13 the combustion gases are exhausted at sonic velocity from the end of the duct 14. The reactants in this case are introduced by contrastream injection through duct 15; the opposing of two high velocity streams, as in this case, leads to extremely rapid and thorough mixing. A suitable reaction time is determined by the size of reaction chamber 16. Another variation in this embodiment of the invention consists in the method of cooling. Since the mixture of combustion gases, reactants and reaction products can be at high pressure, it becomes feasible to accomplish a good portion of the cooling thereof, in order to quench the reaction, by expanding in a heat engine such as turbine 17. This method of cooling is very rapid and homo geneous in the sense that cooling is uniform throughout the gas mixture and does not depend upon contact with a surface, whether water spray or heat exchanger. Moreover, useful amounts of power are recovered from the turbine. Although sufficient cooling to quench the reaction mixture can be obtained by expansion through the turbine, further cooling in order to facilitate separation of the desired products can be secured by contact with coolant spray from the nozzle 18 after the turbine.

Fig. 4 shows a method of practicing the invention in which the reactants are introduced along with the fuel and oxidant directly into the combustion chamber. In this case very intimate contact of reactant with the combustion gases is assured. This configuration is particularly useful when partial oxidation products of hydrocarbons are desired. In fact, the reactant and fuel can be the same chemical species. For example, natural gas and air may be introduced under pressure into the duct 1 containing a stabilizing bafile 2. Part of the natural gas is burned, thus providing heat for promotion of the reaction of another part of the natural gas with some of the oxygen of the air to form formaldehyde. The

the combustion products and the reactant stream being" adjusted to give the required temperature in the resulting mixture. After a desired reaction time, determined by the velocity and distance of flow through chamber 4, the stream encounters a cooling spray obtained by introduction of a coolant, e. g. water through tube 6 toil.

spray nozzle 7. Thereafter, the mixture of combustion gases, reactants, reaction products, and coolant is passed to a suitable separating means which is not shown. The whole of the apparatus can be water-jacketed so that ordinary materials of construction such as steel can be usedtiv without damage.

In Fig. 2 as in Fig. 1 fuel and excess oxidant are introduced under pressure into a duct 1 containing a flame stabilizing bafile 2 and are burned. In this case, however,

secret in obtaining good yields of formaldehyde lies in very rapid quenching of the reaction, since formaldehyde decomposes very rapidly at high temperatures into water and carbon monoxide. In point of fact the expansion which naturally takes place after critical flow the reactant is introduced into the hot combustion products through the tube 8 before sonic velocity is reached at in throat 19 does effectively stop further reaction. The reason for this is that the static temperature of the stream drops abruptly upon expansion to high velocity. the static temperature drop being equivalent to the increase in kinetic energy of flow due to the increase in stream velocity. Since the static temperature, i. e. kinetic energy of the molecules due to random motion, is the controlling factor in chemical reaction rate, the sudden conversion of random energy (temperature) into velocity energy (flow) upon expansion through the nozzle 19, effectively lowers the temperature and therefore the reaction' rate so that the mixture is quenched.

Of course, in such a case when the stream velocity is slowed down subsequently, at least a substantial portion of the velocity energy is reconverted to static temperature which would result in further reaction. However, if a coolant is sprayed into the stream while it is at high velocity the mixture will be cooled sufliciently so that the temperature rise upon slowing down the stream will not be sutlicient to start reaction again. This is the reason for coolant spray 20.

Fig. 5 shows an arrangement in which first the reactant and then the coolant are injected through nozzles 33 and 34 respectively into the hot combustion gases prior to their attainment of sonic velocity at throat of nozzle 21. Here advantage is again taken of the low ering of static temperature upon expansion through a nozzle, with the added advantage that coolant is already dispersed through the stream so that good contact and further cooling of the mixture after expansion will occur rapidly.

Fig. 6 illustrates an embodiment of the invention in which the combustion gases are expanded after reaching sonic velocity in 'the throat of nozzle 22. The resulting supersonic stream aspirates the reactant by familiar jet pump action through inlet duct 23 and mixes thoroughly therewith in the reaction zone 24. The cooling means shown here comprises introducing the reaction mixture beneath the surface of a body of a coolant liquid, e. g. water maintained in container 25. The high velocity of the mixture brings about excellent contact with the water and provides for rapid cooling.

Fig. 7 represents a variation of the invention in which quenching of the reaction mixture is obtained by dilution with further reactant. Fuel and oxidant are introduced under pressure as before into the burner 1, and after being burned are expanded to supersonic velocity through nozzle 27. The high velocity stream of hot combustion gases then entrains reactants introduced through duct 28 and the resulting mixture is allowed to react for a time depending upon the length of duct 29 comprising the mixing zone. In this case the pressure in burner 1 must be sufficiently high so that even after expansion through nozzle 27 and entrainment of reactant, the pressure in reaction zone 29 will be sufficiently higher than the pressure in quenching zone 30 so that sonic velocity will also be obtained in throat'of nozzle 31. Excess reactant, sufiicient to cool the overall mixture below reaction temperature, is permitted to enter through duct 32 and is entrained and mixed with reaction mixture leaving nozzle 31, thereby quenching the reaction mixture in quenching zone 30. Thereafter the mixture is led to suitable separating means (not shown). This configuration is particularly adapted to a recycling operation in which a portion of the excess reactant can be separated and returned as fuel to the burner. Relatively pure oxygen would be the desired oxidant under these conditions since the problem of removing large quantities of diluent nitrogen, present when air is the oxidant, would be eliminated.

The above illustrations indicate to some extent the variety of arrangements of apparatus to which the invention is adapted. There are many other possible configurations which take advantage of the essential features of the invention. The important and novel feature is the use of very high flow velocities, preferably sonic velocities, at the exhaust of the burner which is providing the heat necessary to bring about the desired reaction. This condition of sonic flow, or choking, at once provides for stability in the combustion of fuel and oxidant by making the burner insensitive to pressure variations downstream from the exhaust, permits flexibility in the control of mass flow through the burner by simple adjustment of the combustion chamber pressure, and makes possible very rapid and uniform heating and cooling of the reactants under controlled conditions because of the high velocities and pressures. Furthermore, if a portion of the cooling is accomplished by expansion through a heat engine, a substantial amount of power can be recovered which represents a considerable saving over other processes which involve the use of combustion gases as a direct heating means. Only by operating at relatively high pressure ratios can the heats of combustion and reaction be directly and readily recovered as power. Most important, however, is the nature of the control of reaction time which can be effected on account of the high velocities. When it is considered that in oxidation reactions of hydrocarbons, for example, the reaction time to go all the Way to carbon dioxide and water is of the order of small fractions of milliseconds, it is apparent that in order to spread the reaction zone to reasonable dimensions so that quenching of the reaction at intermediate stages becomes possible, velocities of the order of thousands of feet per second are necessary. The present invention provides a means of obtaining such velocities. The necessity for rapid cooling also is apparent, and the relatively high pressure ratios and velocities available when practicing the invention make this possible. Similar considerations obtain in many other high temperature reactions since reaction rates in general are an exponential function of temperatures.

Thus far the invention has been discussed generally in relation to its principles of operation. It will be apparent that its scope is not limited to any particular set of conditions but that advantages will be applicable to many circumstances. However, the practice of the invention is particularly adapted to certain processes. Any fueloxidant system which gives rise to gaseous products can be used as a heat source for chemical conversion processes. However, only a few are of practical importance because of availability and cheapness. Air of course is the cheapest oxidant, and its use is well adapted to practice of the invention. There is required only sufficient pumping capacity to provide the necessary quantities at the pressures desired in the combustion chamber in order to obtain high velocity conditions at the exhaust. The main disadvantage in using air resides in the large quantity of diluent nitrogen, which complicates subsequent separation steps after the reaction. This diificulty can be avoided if relatively pure oxygen is used as the oxidant, since the combustion products are water and carbon dioxide, which are relatively easily removed from the reaction mixture. The question as to Whether air or oxygen should be used will be determined by the costs of the material relative to the costs of subsequent separation of the reaction products. Either of these oxidants is admirably adapted to the practice of the invention.

\Vith respect to the fuels to be used, fundamentally it is only necessary that the combustion products be essentially gaseous. Since the heat generation step can be carried out entirely independently of the oxidation reaction step, a wide freedom in the choice of fuel while using the most desirable reactant without consumption of the latter for heat generation is provided. Again, however, economic considerations will dictate the choice. Wherever natural gas is readily available, its use is desirable because of the low cost. However, liquid hydrocarbons, water gas, producer gas, blast furnace gas, or even coal may be employed. The main difficulty in using coal or other solid fuels is in feeding them to the combustion chamber under pressure. Liquids or gases are readily pumped in against pressure whereas the movement of solids against a pressure head is more diflicult. If hydrogen is available together with cheap oxygen, the practice of the invention is very advantageous because of the fact that water is the only combustion product, and it is very readily separated from the reaction mixture. In this connection, mention should be made of the oxidant fuel ratios preferably employed in the practice of the invention. We have found that in most cases it is desirable to have an amount of oxygen present that is at least stoichiometrically equivalent to the quantity 'of fuel.

Usuallyan excess is-used such that the combustion gases willcontain :all or a substantial part of the oxygen necessary to convert the .reactant .into its desired oxidation product; however it will be understood that a part or all of the additional oxygen may be introduced after the burner if desired. This additional oxygen may be introduced into the stream of combustion gases at the point of introduction of the hydrocarbon reactant, or ahead of or following this point, or by any desired combination of these procedures.

Temperature can also be controlled to some extent by adjustment of the oxidant to fuel ratios. Maximum temperatures are obtained when stoichiometric or slightly fuel-rich mixtures are employed. Lower temperatures result if the mixture is on the lean or rich side. Where the oxidizing or reducing nature of the combustion products is important, however, temperature must be controlled largely by the relative mass flows of combustion products and reactants and by controlling the preheat of the air-fuel mixture or the reactant stream, or both. There is also the possibility (not illustrated) of injecting a coolant such as water before mixing the combustion products with the reactant stream. This latter expedient is of particular advantage when a neutral stream of combustion products at a temperature lower than the flame temperature is desired.

The separation of the heat generation from the reaction also makes possible a wide range of control of the composition of the reaction mixture. For example, in the production of formaldehyde by using hydrogen or natural gas as fuel and methane or natural gas as the reactant it is possible to provide a high temperature gas stream having a low carbon dioxide content and a high water content while having a high methane to oxygen ratio in the reactant itself.

This separation also makes possible complete utilization of the fuel since it can be completely burned before the reactant is introduced thus providing a high thermal efiiciency in utilization of fuel independent of the reaction desired. It also makes possible a wide range of reactant flows since it is not necessary to maintain composition within the limits of flammability in the reaction zone as in certain prior processes.

The principles of the invention are more particularly illustrated in the following examples.

Example I A mixture of substantially pure oxygen and natural gas in the proportions of two to one by weight are introduced and burned at the rate of one lb. per sec. in a two-inch water-jacketed duct similar to the duct 1 shown in Fig. 4, the distance between the battle 2 and the exit nozzle 19 being six inches, and the diameter of the nozzle throat being 1.5 inches. The exhaust gases attain sonic velocity in the throat of the exit nozzle and are expanded to supersonic velocity downstream therefrom. A spray of water is injected at nozzle 20 located three inches downstream from the exit end of the nozzle. The resulting mixture is led to a suitable separating means (not shown) wherein substantial quantities of formaldehyde are recovered.

Example 2 A stoichiometric mixture of oxygen and methane preheated to 400 K. is burned in the apparatus described in Example 1. The oxyhydrogen pilot provides 2% of the heat imparted to the system. At a point 2% inches upstream from the reaction chamber 4 methane, preheated to 400 K. is injected at the rate of .465 lb./sec. through six stainless steel tubes equidistantly spaced around the circumference. The reaction gases .at the end of the reaction chamber, at a temperature of about 1250 K. are quenched with a water spray and provide a synthesis gas containing hydrogen and carbon monoxide .in the ratio of two to one.

.By adjusting the water spray used for quenching to a mass .flow-of .l...103.1bs./sec. whereby the temperature of the;gases is lowered from about .1250 K. .to about 675 K., and passing the resulting gaseous mixture through a second :reaction chambercontaininga catalyst :activating the conversion of carbon monoxide and water to carbon dioxide and hydrogen, a hydrogen and carbon dioxide containing gas having a very low. carbon monoxide content is produced.

There are many modifications possible in conjunction with the practice of the invention which will be apparent to those skilled in the art and have not .been discussed in detail. For example, preheating the reactant feed stock to some .temperature below that at which rapid reaction takes place and using the combustion products only for the final temperature rise may simplify subsequent separation steps by reducing the proportion of combustion products present in the reaction mixture. Further, by preheating the oxidant .and fuel before entrance into the combustion chamber, considerably higher temperatures and velocities can be obtained in the exhaust stream. Thus preheating to temperatures of the order of .1000 K. Or-higher may be desirable, the upper limit for. preheating being determined practically only by materials of construction and coking of the hydrocarbon feedstocks. The use of burnersof the type used in turbojet power plants are suited to particular installations. Withsuch a burner, part of the energy of the combustion reaction is useddirectly to .pump air to the burner in order to get the desired pressure level.

Catalysts may be employed in the reactions by introducingthemin finely divided .form with the fuel or oxidant or reactant or by interposing the catalyst in fixed position in the path of the gases.

These andmany other modifications are possible without departing from the principle of the invention which is the introduction of a hydrocarbon reactant into hot oxygen-containing combustion ,gasesin an elongated chamber in at leasta portion of which the gases flow at a high velocity, at least 1000 feet per second, and preferably at sonic velocity or vover, and thereafter quickly cooling the reaction gases and recovering the reaction product therefrom.

Although the use of sonic velocities in the combustion gases used for heating the reactants is very advantageous in-t'he practice of the invention,.it is not always necessary that this condition of critical .fiow exist. It is sometimes possible to obtainthedesired mixture and reactiontime-space relationshipsat velocities that are considerably below sonic velocity. .The essential feature of the invention consists in taking advantage of the rapid and uniform mixing .between hot combustion gases and reactants when the former are flowing at .high velocity at the time of admixture with the latter. We have found that velocities as low as "1000 feet .per second can provide thisrapid mixing. Depending upon .the temperature of the gases, 1000 feet per second can be almost any fraction .of sonic velocity. Below this value the mixing rates begin to drop off. When subsonic flow velocities are employed certain of the advantages of sonic velocity, such as shielding the combustion zone from downstream pressure fluctuations, are lost. However, for some reactions in which the rates are not too rapid so that velocities of 1000 feet per second will provide sufficient extension of the reaction zone in space to permit adequate control, it may be desirable -to employ these lower than sonic velocities in order to decrease pumping or compressor costs.

Example 3 Methane and air .in proportions of one to 20 by weight .are burned at a rate of 1.2 pounds per second in a two inch duct arranged according to Figure .2. Benzene is introduced through the reactant inlet comprising a spray nozzlemounted coaxiallytin the duct six inches upstream .from the duct exit and facing upstream. Ihe benzene flow rate is about 0.4 pound per second. After quenching with the water spray, substantial quantities of phenol along with some biphenyl are recovered from the effluent.

Example 4 Natural gas and air in stoichiometric proportions are burned at a rate of 1.3 pounds per second in a waterjacketed two inch duct arranged as in Figure 1. The length of the combustion zone is 22 inches. A mixture of toluene and air preheated to 250 degrees C. and containing 20 per cent toluene by weight is introduced through the reactant port as shown at a rate of 0.5 pound per second. The reaction section comprises a 4 inch duct 4 feet long. A water spray at the end of the reaction zone rapidly cools the stream to about 100 degrees C. Substantial quantities of benzoic acid are recovered from the efiiuent.

In addition to the examples described above, this method is of great interest in connection with the production oi maleic anhydride from benzene, phthalic anhydride from ortho-xylene or naphthalene, formaldehyde from propane and/or propylene and fatty acids from parafiin hydrocarbons such as kerosene.

This is a continuation-in-part of our application Serial No. 165,762 filed June 2, 1950, now abandoned, and of our pending application Serial No. 265,292 that was filed on January 7, 1952, as a continuation-in-part thereof.

What we claim is:

1. A method of oxidizing hydrocarbons to intermediate oxidation products which comprises continuously burning a flowing mixture of fuel and gaseous oxidant within an elongated chamber at a rate effective to produce within said chamber a gas stream having a high temperature zone in at least part of which the gases flow at a velocity of at least 1000 feet per second, reacting hydrocarbons with oxygen in said high temperature zone and thereby converting a substantial proportion thereof into intermediate oxidation products, quenching the oxidation reaction by quickly cooling the gas stream, and recovering the intermediate oxidation products therefrom.

2. A method according to claim 1 in which the gases in the high temperature zone attain sonic velocity.

3. A method according to claim 1 in which the hydrocarbon is an aliphatic hydrocarbon.

4. A method according to claim 3 in which the hydrocarbon is natural gas.

5. A method of producing formaldehyde which comprises partially burning a mixture of methane and oxygencontaining gas at the inlet of an elongated chamber, re-

taining the resulting gas mixture in said chamber only for the time necessary to bring about conversion of the remainder of the methane to formaldehyde and then cooling the gases by immediately passing them through a restricted orifice at substantially sonic velocity and expanding them into a quenching zone, introducing a quenching fluid into the gases in said quenching zone, and recovering the formaldehyde so produced.

6. A method of converting hydrocarbons into intermediate oxidation products which comprises burning a mixture of fuel and oxidant under pressure in a combustion zone, expanding the combustion products in a reaction zone to a static pressure not more than approxi mately half of that in the combustion zone and thereby attaining substantially sonic gas velocities, combining a hydrocarbon reactant with oxygen in said reaction zone at reaction temperature and thereby converting a substantial proportion thereof into intermediate oxidation products, passing the resulting gas mixture into a quenching zone and quickly cooling it therein to a temperature below reaction temperature, and recovering the resulting intermediate oxidation products from the cooled gases.

7. A method of converting hydrocarbons into intermediate oxidation products which comprises burning a mixture of fuel and oxidant under pressure in a combustion zone, expanding the combustion products in a re action zone to a static pressure not more than approximately half of that in the combustion zone and thereby attaining substantially sonic gas velocities, introducing a spray of hydrocarbon reactant into said reaction zone and combining it with oxygen therein at reaction temperatures to form intermediate oxidation products, passing the re sulting gas mixture into a quenching zone and quickly cooling it therein to below reaction temperatures, and recovering the intermediate oxidation products from the cooled gases.

8. A method according to claim 7 in which the gases are cooled by expansion into said quenching zone.

9. A method according to claim 7 in which the gases are cooled by the injection of a coolant liquid into said quenching zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,377,847 Allen June 12, 1945 2,384,028 Hall Sept. 4, 1945 2,608,594 Robinson Aug. 26, 1952 

1. A METHOD OF OXIDIZING HYDROCARBONS TO INTERMEDIATE OXIDATION PRODUCTS WHICH COMPRISES CONTINUOUSLY BURNING A FLOWING MIXTURE OF FUEL AND GASEOUS OXIDANT WITHIN AN ELONGATED CHAMBER AT A RATE EFFECTIVE TO PRODUCE WITHIN SAID CHAMBER A GAS STREAM HAVING A HIGH TEMPERATURE ZONE IN AT LEAST PART OF WHICH THE GASES FLOW AT A VELOCITY OF AT LEAST 100 FEET PER SECOND, REACTING HYDROCARBONS WITH OXYGEN INSAID HIGH TEMPERATURE ZONE AND THEREBY CONVERTING A SUBSTANTIAL PROPORTION THEREOF INTO INTERMEDIATE OXIDATION PRODUCTS, QUENCHING THE OXIDATION REACTION BY QUICKLY COOLING THE GAS STREAM, AND RECOVERING THE INTERMEDIATE OXIDATION PRODUCTS THEREFROM. 